Res. Chem. Intermed.
, Vol. 28, No. 2,3, pp. 101–116 (2002)
Also available online - www.vsppub.com
EPR study of iron-doped MFI zeolite and silicalite
catalysts: effect of treatments after synthesis
ANNA M. FERRETTI
, LUCIO FORNI
, CESARE OLIVA
and ALESSANDRO PONTI
Università di Milano, Dipartimento di Chimica Fisica ed Elettrochimica, Via C. Golgi 19,
I-20133 Milano, Italy
Consiglio Nazionale delle Ricerche, Centro per lo Studio sulle Relazioni tra Struttura e Reattività
Chimica, Via C. Golgi 19, I-20133 Milano, Italy
Received 29 October 2001; accepted 3 December 2001
Abstract—The systematic study of iron-doped MFI zeolite and MFI silicalite by X- and Q-band EPR
spectroscopy is reported in this paper. Both samples, which contain Fe(III) ions in the MFI lattice,
underwent three sequential treatments — calcination, steaming, and washing with sodium dithionite
solution — which are needed to make the catalyst active by extracting iron ions from the lattice.
EPR spectra could be simulated by assuming a broad distribution of spin– spin (zero- eld) coupling
parameters. The simulation parameters depend on sample history and reproduce the selective intensity
changes that are observed in X-band spectra after each treatment. In particular, the distribution width
decreases by calcining and steaming samples and then it increases by treating with aqueous dithionite
solution. This is in agreement with the view that iron ions are extracted from the framework by
calcining and by steaming and may form relatively large iron oxide particles which become smaller
after the chemical treatment. We have also studied the temperature dependence of the EPR spectra.
The most interesting results are from the steamed samples. Their behavior has been interpreted as due
to the presence of superparamagnetic single domain particles of iron oxide. This agrees with the view
that iron oxide particles form during steaming.
: EPR; catalyst; iron-doped MFI zeolite.
Iron-containing zeolites and silicalites with MFI structure have attracted consid-
erable interest since 1988, when three groups of researchers [1–3] independently
found that, in these catalysts, Fe(III) plays a fundamental role in the oxidation reac-
tion of benzene to phenol [4– 6]. Since Fe(III) is paramagnetic, EPR spectroscopy
is a good method to study iron-containing active sites in these catalysts.
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